The present invention relates to an optical multiplexer/demultiplexer using an arrayed waveguide grating.
Recently, studies and development of optical frequency division multiplexing communications are being actively made in optical communications as means for significantly increasing the transmission capacity. Significantly increasing the transmission capacity in optical communications requires an optical device which can multiplex and demultiplex light having multiple wavelength components with as small a wavelength interval as possible. As one such means is known an optical multiplexer/demultiplexer using an arrayed waveguide grating (e.g., Japanese Unexamined Patent Publication (KOKAI) No. Hei 9-49936, etc.).
This optical multiplexer/demultiplexer has a plurality of input waveguides, an input-side slab waveguide, an arrayed waveguide grating having a plurality of waveguides, an output-side slab waveguide and a plurality of output waveguides connected in the named order. And, this optical multiplexer/demultiplexer transmits, for example, wavelength-multiplexed light (center wavelength xcex1 to xcex8, wavelength interval xcex94xcex) inject to a specific one of the input waveguides to the input-side slab waveguide, then to the arrayed waveguide grating having a plurality of waveguides, and then to the output-side slab waveguide to demultiplex it to lights of center wavelengths xcex1 to xcex8, and outputs them to the determined waveguides in the plurality of output waveguides.
At the time of fabrication processing waveguides of the arrayed waveguide grating, the widths, heights and refractive indexes of the waveguides to be fabricated vary so that the center wavelength of the light that is demultiplexed by the output-side slab waveguide is likely to deviate from the designed value.
At this time, if the deviation of the center wavelength of the light from the design value is a given deviation amount from a pre-designed, predetermined center wavelength even if the arrayed waveguide grating differs, the deviation is correctable when dealt with at the design stage and does not raise a problem. If the deviation of the center wavelength differs from one manufactured optical multiplexer/demultiplexer to another, however, it cannot be corrected. What is more, such deviation of the center wavelength usually differs from one arrayed waveguide grating to another.
For an optical multiplexer/demultiplexer using an arrayed waveguide grating, therefore, it is difficult to previously estimate the deviation of the center wavelength after production, which is a factor to considerably reduce the production yield of optical multiplexers/demultiplexers.
Accordingly, it is an object of the present invention to provide an optical multiplexer/demultiplexer which can adequately correct a deviation of the center wavelength to ensure multiplexing and demultiplexing of wavelength-multiplexed light even if an arrayed waveguide grating is used, and which can be produced at a low cost with a high yield.
To achieve the above object, according to this invention, an optical multiplexer/demultiplexer having a plurality of first waveguides, a first slab waveguide, an arrayed waveguide grating having a plurality of waveguides, a second slab waveguide and a plurality of second waveguides, said individual waveguides being connected in the above-said order, is constituted in such a way that a ratio of a distance between the plurality of first waveguides at a connecting portion with the first slab waveguide to a distance between the plurality of second waveguides at a connecting portion with the second slab waveguide differs from a ratio of a focal length of the first slab waveguide to a focal length of the second slab waveguide.
Preferably, it is constituted in such a way that the distance between the plurality of first waveguides at the connecting portion with the first slab waveguide is equal to the distance between the plurality of second waveguides at the connecting portion with the second slab waveguide; and the focal length of the first slab waveguide differs from the focal length of the second slab waveguide.
Or, preferably, it is constituted in such a way that the distance between the plurality of first waveguides at the connecting portion with the first slab waveguide differs from the distance between the plurality of second waveguides at the connecting portion with the second slab waveguide; and the focal length of the first slab waveguide is equal to the focal length of the second slab waveguide.
The center wavelength used in this specification means the center wavelength of light which has been demultiplexed from wavelength-multiplexed light.